How hard would it be to kill the highlights entirely? Add just one slider that represents 0% to 100% highlights. It would be interesting to create additional artistic effects particularly when these effects are blended in using the tube paint tools and paint brush tool.
For instance, imagine using the tube paint over a fine powdery looking layer texture setting with no highlights.
I am sure there are other forms like this as well from other cultures.
Besides representing different artistic mediums it also would be nice to have this for oil paintings as well because not everything is well highlighted in reality and this better serves making to paints look more real according to the environment type the artist wants to represent where light either can be strong and bright therefore more shininess or more diffused in a more dimmed and moody environment to how the lighting reacts to the surface of paint.